Recently, new and highly-active supported titanium catalysts based upon the use of magnesium alkoxides have become available for the commercial production of polyethylene. For example, German Offenlegungsschrift No. 2,123,356 teaches polymerization of ethylene and mixtures thereof with an aluminum alkyl compound co-catalyst and a catalyst component made from a magnesium dialkoxide, a titanium (IV) compound and an aluminum alkyl halide. U.S. Pat. No. 3,901,863 teaches catalyst components made, inter alia, from magnesium and titanium alkoxides and alkylaluminum dichlorides which are promoted with an alkylaluminum compound. Many of these catalysts, however, create serious problems in the particle-form and vapor phase polymerization processes because the particle size of the polymeric product is so fine that difficulties are encountered in the separation and handling of the products; particularly, trouble occurs in the extrusion and compounding steps involved in producing a commercial product. Now a method has been found to keep the high activities of certain of these new generation ethylene polymerization catalysts and yet produce polymer of sufficiently large particle size so that the above-referred to problem is reduced or eliminated completely. The solution to this problem involves a simple variation in the process of manufacture of the solid catalyst component.